Plastic encased coil



April 14, 1959 A. P. HULTGREN 2,882,504

PLASTIC ENCASED COIL Filed Oct. 13, 1955 United states Patent "ice PLASTIC EN CASED COIL Arnold P. Hultgren, River Forest, Ill., assignor toAmerican Molded Products Co., Chicago, 11]., a corporation of Illinois Application October 13, 1953, Serial No. 385,754

3 Claims. (Cl. 336-96) This invention relates generally to a construction and method of potting electrical coils within a plastic resin, and more particularly to a construction and method of making a unitary coil assembly comprising a mold together with a cooperating coil, and bobbin, arranged to receive a coil-encasing filling of plastic resin.

it is one of the objects of the present invention to provide a coil construction for hermetically sealing and moistureproofing an electrical coil to permit its use in environments wherein moisture may be present, such as, by way of example and not limitation, in washing machines, dishwashers, driers, and the like.

Another object of the present invention is to provide a method for potting coils which is adaptable to large scale production without the necessity of costly replaceable metal or rubber molds.

It is a further object of the present invention to provide a simple and low-cost coil construction wherein the electrical terminals and lead wires are embedded in insulating material, whereby a proper and permanent electrical connection may be maintained, and corrosion due to moisture and to presence of acids in solder fluxes is avoided.

It is still another object of the present invention to provide a simple and low-cost coil construction wherein the electrical terminals and the lead wires are rigidly encased so as to prevent relative movement and Wear therebetween, and to avoid accidental breakage.

It is a still further object of the present invention to provide a rigidly reinforced coil construction wherein possible deformation of the core due to heating as a result of frequent energization during use is prevented.

It is another object of the present invention to provide a simple and low-cost coil construction wherein the coil is wholly embedded within an insulating resin in such a manner as to eliminate corona eflects in high voltage applications.

The above and other objects and features of the present invention will be more readily apparent from the following description when read in connection with the accompanying drawing wherein:

Figure l is a perspective view of a unitary coil assembly embodying the present invention.

Figure 2 is an end elevation showing the mold and interfltting bobbin of Figure 1 in disassembled relation.

Figure 3 is an end elevational view, partly in section, showing a completed core assembly of the type illustrated in Figure 1.

Figure 4 is a cross-sectional view, taken along line d-4 of Figure 3.

Figure 5 is a top plan view of a modified, unitary coil assembly constructed in accordance with the present invention, wherein the coil is of different geometric form from that shown in Figures 1 to 4.

Figure 6 is a cross-sectional view, taken along the line 6-6 of Figure 5.

Figure 7 is a cross-sectional view showing a modifica- 2,882,504 Patented Apr. 14, 1959 tion of the construction shown in Figures 5 and 6 wherein the mold is of different form.

The conventional practice of the prior art in potting of electrical coils requires the use of rubber or metal molds in which the wire-wound coil is supported and into which a plastic resin or other insulating material is introduced. Such resins are generally of the phenolic or epoxy type, or other suitable material of high dielectric constant, and require from 4 to 6 hours to effect a relatively hard setting. It will be apparent, therefore, that such former practice necessitates the use of roughly half as many molds as the number of coil assemblies to be produced in a single day. Metal molds are costly and their removal from the completed assembly is diflicult and timeconsuming. Rubber molds, in addition to being costly, are subject to tearing during the stripping operation and are therefore limited in life to about 4 or 5 uses. The present invention contemplates the use of an inexpensive and permanent plastic shell which permits coils to be potted in a manner so that substantial investments in mold parts and the high cost of time-consuming mold stripping are eliminated. When applied to large volume production rates as high as 5000 units per day, it will be apparent that the potting arrangement of the present invention permits substantial savings in production costs over the former practice in the art.

Referring more particularly to Figures 1 to 4 of the drawing, there is shown a potted coil assembly, indicated generally at 1. For coil windings of this type, I have devised a cooperating mold and bobbin wherein the bobbin is introduced laterally into the mold, as will hereinafter be described in greater detail. The assembly comprises a mold 3 of. generally cylindrical form, and U- shape in cross-section, preferably having a pair of opposed flat side portions 5, and a bottom wall 7 of semicircular cross-section. The side portions 5 and bottom wall 7 cooperate to form a trough therebetween. The mold 3 is provided with a pair of U-shaped end flanges 9. Four studs or supporting legs 11 extend downwardly from the bottom wall 7 and provide support means for holding the. mold 3 in horizontal position upon a flat surface to facilitate the filling operation, as will hereinafter appear.

A bobbin 15 is provided to snugly engage and fit within the mold 3. The bobbin l5 includes a hollow cylindrical core 17 terminating in attached end flanges 19. The core and end flanges may be integrally formed as a unitary construction, or may be assembled from separate pieces. The end flanges 19 are of generally U- shaped form and have a raised rib or bead 21 providing an outwardly projecting abutment means. The core 17 of the bobbin 15 is of substantially the same length as the inner longitudinal dimension of the trough formed by the mold 3, and the end flanges 19 substantially conform in size tothe inner dimensions of the end shoulders formed between flanges h and the walls 5 and 7 of the mold 3. The ribs 21 are so positioned on the end faces of. the flanges 1-9 that their inner edges closely conform to and engage the inner edges of the flanges 9 of the mold 3 to form a liquid-tight seal. It will be apparent that insertion of bobbin 15 into mold 3 results in a snug, contacting engagement of each flange l9 and rib 21 with the inner face and edge respectively of a flange 9, corresponding in such a manner that the possibility of leakage of a liquid from the trough formed by mold 3, outwardly past the axial ends of the assembly, is effectively prevented.

As an. alternative form of simple construction, the mold 3 may be dispensed with as a unitary means cooperating with the bobbin to provide a trough, and a trough may be formed by directly winding or otherwise applying strips of adhesive or masking tape to the end flanges of the bobbin so as to provide a U-shaped Wall between the end flanges and around the core of the bobbin. In this manner a structure of shape substantially similar to the interfitting mold 3 and bobbin 15 may be formed by merely building up an outer wall upon the bobbin alone, with tape or some similar material, thereby eliminating the use of a separate mold entirely.

The bobbin 15 is wire Wound in conventional manner, as best shown in Figure 4, so as to form a coil 23, having terminal end wires 25 projecting upwardly therefrom. The completed coil assembly then may be inserted within the mold 3 in the manner heretofore described. A suitable plastic resin 27 of high dielectric constant may next be introduced in fluid or mastic form to the mold so as to substantially fill its contained volume and fully surround the coil, with the wires 25 permitted to extend upwardly through the top surface of the resin. Upon setting of the resin, the coil, bobbin and mold become integrally bonded together as a permanent unitary assembly, havin the desirable properties and characteristics previously set forth above.

The mold 3 and bobbin 15 are preferably formed from an inexpensive, suitable thermo-plastic material, such as styrene. The cost of the molds 3, which become a permanent part of the assembly, is so small that great savings are eifected over current methods of production of potted coils.

In Figures and 6 I have illustrated a second embodiment of the present invention, differing from the form illustrated in Figures 1 to 4 because of the geometric requirements of the coil. The coil to be potted in the construction illustrated in Figures 5 and 6 is of the disc-shaped type wherein the longitudinal axis of the coil is very short relative to the diameter. The assembly comprises a shallow, annular, cup-shaped mold 103. having a fiat bottom 104 and a side wall 106. The mold 103 is provided with a central aperture in the bottom wall around which is an upwardly extending flange 105, which cooperates with the bottom wall, at the aperture, to form a shoulder, 105a. A tubular sleeve, or bobbin 117, is adapted to seat tightly upon the shoulder 105a and within the flange 105, to form a liquid-tight seal. The side wall 106, is provided at its upper portion with an outwardly extending step having a bottom wall 107 and a side wall 108. It will be apparent that the step portion serves to provide an increased mold diameter at the upper portion remote from the bottom wall 104. The coil designated as 123, is wound in a conventional manner about the bobbin 117 and has an upwardly and outwardly extending terminal lead wire 125. The coil 123 and bobbin 117, as an assembly, are inserted within the mold 103, and the end of the bobbin 117 is snugly and firmly seated on the shoulder 105a within the flange 105. with the coil spaced from the bottom and side wall of the mold 103. Suit-able fluid resin 127 is then poured into the mold so as to wholly cover the coil. The resin filling is poured to a suflicient height to permit overflow into the increased diameter stepped portion, as indicated at 127a. Upon setting of the resin an integrally bonded unitary assembly is provided.

The purpose of the increased diameter stepped portion heretofore described, is to prevent or reduce corona effects while at the same time requiring a minimum of resin material to be utilized. As is well known, Where corona eflects are substantial, there is a tendency to break down the insulating material and which causes breakdown of the coil. It will be apparent that the distance between the upper sharp outer edge of the coil and the upper outer corner of the insulating resin is substan' tially greater because of the step portion than would be the case if the side wall 106 were not provided with such a construction.

In Figure 7 I have illustrated a modification of the construction of coil assembly of the type shown in Figures 5 and 6. The assembly comprises an annular,

cup-shaped shell 203, having a bottom wall 204, an upturned inner flange 205, to provide a seating shoulder 205a for a bobbin 217, and a side wall 206. In this construction the side wall 206 is not provided with the step construction illustrated in the embodiment of Figures 5 and 6. It will be apparent that the employment of this form of construction necessitates a filling of resin 227 to a substantially greater height above the top portion of the coil 223 so that the distance between the upper outer sharp corner of the coil and the outer edge of the resin is sufliciently large to minimize corona effects. A comparison of this form with that of Figures 5 and 6 serves to indicate the advantages of the step construction heretofore described. It will be apparent that the embodiment of Figure 7, while simpler in form than that of Figures 5 and 6, requires the use of asubstantially larger quantity of resin to avoid the disadvantages of corona efiects.

It will be apparent that the shells 3, 103 and 203 are unitary and self-supporting without the need for any mold-holding means. Shell 3 stands upon its legs 11, and may be handled as an individual unit. Similarly, shells 103 and 203 are stable and self-supporting upon their flat bottom walls 104 and 204, respectively. In this manner, each mold may be readily handled as a separate and distinct unit, which serves to greatly facilitate filling operations by permitting the molds to be arranged in any desired pattern, or in a discrete series upon a conveyor or the like. By virtue of the constructions embodying the present invention, the soldered connections of a terminal Wire to the coil are totally embedded in the resin and insure maintaining proper electrical connections. Furthermore, air is kept out of contact with the soldered joints and avoids corrosion effects due to acids in the solder fluxes and insure mechanical strength of the soldered joints. The potting resins also serve to stabilize and hold wires of the coil in proper position and prevent possible breaking or wear of insulation which might cause short circuiting. Potting of electrical coils reinforces and rigidifies the coil and bobbin and eliminates possible deformation which sometimes occurs when coils develop excessive heat caused by frequent energization, and which deformation might cause bending or sticking when the coil is part of a solenoid.

While I have herein shown and described several preferred embodiments of my invention, manifestly it is capable of modification and rearrangement without departing from the spirit and scope thereof. I do not, therefore, wish to be understood as limiting this invention to the precise embodiments herein disclosed, except as I may be so limited by the appended claims.

What is claimed is:

1. A sealed coil construction comprising an integrally unitary bobbin of thermoplastic material having a core and a pair of spaced apart end flanges attached to said core, said bobbin flanges having outwardly projecting abutment means thereon, a coil of wire wound around said core between said flanges, an integrally unitary shell body of thermoplastic material and of upwardly-open channel form having an inwardly extending generally U-shape flange around each end thereof, said bobbin flanges being matingly received within the shell flanges in substantially full and liquid-tight engagement with the inner surface of said shell flanges, said abutment means seating upon the edges of said shell flanges and efiecting predetermined positioning of said bobbin within said shell, thereby to form a mold and to support the coil in spaced apart relation to the shell body, and a body of electrical insulating material, initially in a fluid state, and capable of subsequent setting to a relatively hard state, filling the mold and completely surrounding the surface of the coil and thereby forming a unitary assembly.

2. A sealed coil construction comprising an integrally unitary bobbin of thermoplastic material having a core and a pair of spaced apart end flanges attached to said core, said bobbin flanges having outwardly projecting abutment means thereon, a coil of wire wound around said core between said flanges, an integrally unitary shell body of thermoplastic material and of upwardly-open channel form having an inwardly extending generally U- shape flange around each end thereof, said bobbin flanges being matingly received within the shell flanges in substantially full and liquid-tight engagement with the inner surfaces of said shell flanges, said abutment means seating upon the edges of said shell flanges and elfecting predetermined positioning of said bobbin within said shell, thereby to form a mold and to support the coil in spaced apart relation to the shell body, and a body of electrical insulating material, initially in a fluid state, and capable of subsequent setting to a relatively hard state, filling the mold and completely surrounding the surface of the coil and thereby forming a unitary assembly, said shell body having a plurality of depending feet to support said assembly in an upright position for the reception and during hardening of said insulating material.

3. A sealed coil construction comprising an integrally unitary bobbin of thermoplastic material having a core and a pair of spaced apart end flanges attached to said core, said bobbin flanges having outwardly projecting continuous rib means thereon, a coil of wire wound around said core between said flanges, an integrally unitary shell body of thermoplastic material and of upwardly-open channel form having an inwardly extending generally U-shape flange around each end thereof, said bobbin flanges being matingly received within the shell flanges in substantially full and liquid-tight engagement with the inner surfaces of said shell flanges, said rib means seating upon the edges of said shell flanges and efiecting predetermined positioning of said bobbin within said shell, thereby to form a mold and to support the coil in spaced apart relation to the shell body, and a body of electrical insulating material, initially in a fluid state, and capable of subsequent setting to a relatively hard state, filling the mold and completely surrounding the surface of the coil and thereby forming a unitary assembly.

References Cited in the file of this patent UNITED STATES PATENTS 1,880,821 Connor Oct. 4, 1932 2,421,444 Tyne June 3, 1947 2,464,568 Flynn et a1. Mar. 15, 1949 2,640,102 Woods et a1. May 26, 1953 2,775,74 Bogue Dec. 25, 1956 

